A precursor for ZrB2 ceramic was successfully synthesized in a chemical reaction between polyzirconoxanesal (PZS) and boric acid. The molecular structure of the precursor, thermal properties and the pyrolysis behavior of the precursor were investigated. The results showed that the as-synthesized precursor was a polymer based on Zr-O-C-B bonds. The precursor was stable in air atmosphere and soluble in common organic solvents. The ceramic yield of the precursor at 1200 degrees C was around 65.5 % under N-2 atmosphere. The derived ceramics obtained at 1200 degrees C were composed of B2O3, ZrO2 and carbon. When the temperature was increased up to 1300 degrees C, peaks of ZrC emerged owing to carbothermal reduction. m-ZrO2 and t-ZrO2 disappeared when the pyrolysis temperature was increased to above 1400 degrees C. ZrB2 became the predominant phase when the pyrolysis temperature was increased up to 1500 degrees C.